Adhesive and its use

ABSTRACT

The invention relates to the use of a two-phase polymer combination which is dissoluble in aqueous alkali and comprises a. an alkali-soluble copolymer or terpolymer of an α,β-unsaturated monocarboxylic acid which possesses carboxyl groups distributed essentially uniformly over the chain of the molecule, as a continuous phase, and b. a copolymer or terpolymer which is insoluble in aqueous alkali and contains epoxy groups along its polymer chain, as a discontinuous finely disperse phase, c. free epoxy groups on the surface of the polymer particles of the discontinuous phase being linked to one another by esterification with some of the carboxyl groups of the polymer of the continuous phase, and the remaining carboxyl groups being present in unchanged form, as an adhesive. The polymer combination, which is not tacky in the dry state, can be made tacky by supplying aqueous moisture to it.

The invention relates to an adhesive based on a polymer which can bemade tacky in conjunction with aqueous moisture, and to its use.

Industrial products having self-adhesive properties are sufficientlywell known from everyday use; examples are the wide variety of kinds ofsheets and adhesive tapes, used in the packaging, construction orfurniture sector and in the metal, glass and automotive industries,among others, or else office products such as adhesive strips, stickylabels or sticky notes. Common to these products is the fact that forbonding to various substrates they are coated with adhesive on one sideor else, according to their specific application, on both sides.

Production, handling and also the post-use disposal of these coatedself-adhesive products have a number of known drawbacks.

In the case of self-adhesives it is necessary to protect the adhesivelayer with a carrier material, such as siliconized paper, so that itdoes not lose activity prior to use, as a result for example ofcontamination, or, in the case of sheets, that the sheet layers do notstick to one another. Following application the carrier material is leftas non-recyclable waste and therefore constitutes a disposal problem.

The removal of adhesive sheets or sticky labels following theirapplication, from glass or porcelain products, for example, isfrequently associated with severe difficulties. Labels and sheets, forexample, can only be removed manually, while removal of adhesiveresidues is often possible only with great effort, using organicsolvents.

The specific production of tacky sheets without an adhesive coating,based on ethylene-vinyl acetate (EVA) or unplasticized polyvinylchloride (PVC-u) and low-density polyethylenes (LDPE) with correspondingtackifiers, is also known. The bond strength of these sheets is low.Their adhesion is suitable primarily for fixing sheet to sheet, andhence they are of only limited usefulness as wrapping sheets forindustrial packaging and in the packaging of foodstuffs.

There are also water-soluble adhesives. These adhesives have thedrawback that if too much water is used they are diluted or becomedetached and then no longer stick.

The invention provides for the use of a two-phase polymer combinationwhich is dissoluble in aqueous alkali and comprises

-   a. an alkali-soluble copolymer or terpolymer of an α,β-unsaturated    monocarboxylic acid which possesses carboxyl groups distributed    essentially uniformly over the chain of the molecule, as a    continuous phase, and-   b. a copolymer or terpolymer which is insoluble in aqueous alkali    and contains epoxy groups along its polymer chain, as a    discontinuous finely disperse phase,-   c. free epoxy groups on the surface of the polymer particles of the    discontinuous phase being linked to one another by esterification    with some of the carboxyl groups of the polymer of the continuous    phase, and the remaining carboxyl groups being present in unchanged    form,    as an adhesive.

The polymer combination has already been described in EP 0 928 316 B1,the content of which is hereby incorporated by reference. It is known inthe form of a melt, powder and films (foils). WO 98/7778 describesalkali-dissoluble laundry detergent pouches made from films of thepolymer combination.

Surprisingly it has been found that this polymer combination in themoist state is able to form an adhesive bond not only to smooth surfacesbut also to textured surfaces, as for example to glass, metal surfaces,plastics, nonwovens, woven fabrics, paints, paper or else to films ofthe same kind. The bond formed exhibits an extremely high strength withrespect to mechanical forces, after drying, even to the smooth surfaces.In the dry state the polymer itself is not tacky.

The polymer combination can be made tacky by supplying aqueous moistureto it, but is not dissolved in the process. Products comprising thispolymer combination can be bonded without an additional adhesive coatingor can themselves act as an adhesive. The disadvantages and restrictionsdescribed above do not occur in the case of use in accordance with theinvention.

The necessary moisture can be supplied in the form of vapour or liquid,in the latter case by direct or indirect application such as spreading,dropping, pouring or spraying or in atomized form via a nozzle.Moistening in the case of a sheet can be carried out on one or bothsides, in the latter case, for example, by complete immersion of thesheet material in water.

In powder form as well it is possible to use the polymer combination inaccordance with the invention. In that case the powder is preferablydispersed in water and applied to the respective substrate, inparticular by spraying.

Products comprising this polymer combination are stable in acidic andneutral, aqueous media, while in aqueous alkalis it is possible withparticular advantage to dissolve the products completely. Byacidification the polymer combination can be reprecipitated and suppliedto a recycling circuit.

The invention also relates to a method of bonding articles, or bondingto articles, using the polymer combination.

It should be emphasized at this point that alkali-free aqueous moistureis enough to bring about the desired adhesive effect of the polymercombination. By adding alkaline media it is possible to dissolve thepolymer combination on the surface partly or completely; preferably analkaline medium is not provided for application in accordance with theinvention.

The bond of the polymer combination to the surfaces of theaforementioned substrates is still sufficient even in a moistenvironment, provided that no substantial mechanical forces act on thebond. If, however, the bonded polymer combination is wetted with largeamounts of water, the bond can be parted again. In this way the polymercombination can be removed without residue, and this constitutes asubstantial advantage of application in accordance with the invention.

For films and powders comprising the polymer combination there are amultiplicity of possible applications.

In one preferred embodiment a film of the polymer combination is opaque,which can be achieved by incorporating pigments into the copolymer.Thus, for example, a white coloration is obtainable by admixing titaniumdioxide. Without admixtures of pigment the films are transparent tomilky. The films can be covered in places or entirely with at least onecolour layer, in particular by printing. Printing inks used arepreferably those which are soluble in aqueous alkali and preferablyinsoluble in a neutral to acidic medium. Thus films comprising thepolymer combination can be used, for example, as labels without any needfor coating with pressure-sensitive adhesive, such as is necessary, forexample, for the labels described in EP 0 316 676 B1.

Films comprising the polymer combination can be bonded over their entirearea or only in places. They are outstandingly suitable for use as aprotective coating or locally bonded protective covering, particularlyin the case of the transportation and temporary and long-term storage ofgoods and products. There is a need for protective coverings andprotective coatings in numerous sectors and branches of industry,particularly in the aforementioned transport, construction, sanitary orfurniture sector, or else, for example, in the glass, metal orautomotive industry.

Coatings comprising the polymer combination can be produced either bybonding, in the form of a film, or else by application in the form of adispersed powder. A further possible field of application for suchcoatings is that of protection against graffiti. Preference is givenhere to use for protecting transport means such as railway carriages.

If the polymer combination is employed in the form of a film, thethickness and width of the film are guided by the particular end use,and can be adapted accordingly. The film thickness is generally from 10μm to 200 μm; for protective films, in particular, from 25 μm to 60 μmare sufficient. The width can be chosen arbitrarily as a function ofproduction of the film, and is generally between 20 cm and 800 cm, inparticular in the range from 50 cm to 120 cm.

The polymer combination can also be processed in the form of a hot-meltadhesive, particularly in combination with aqueous bonding. In this caseas well a permanent bond is formed to smooth and textured surfaces. Inconjunction with tackifying by supply of aqueous moisture it is possibleto use the polymer combination both in the form of a film and in theform of a powder in a multi-stage adhesion process, in which it becomesmoist in a first step and in a further step is used for hot bonding.

Moist and/or hot bonding of the polymer combination can be employed forthe production of composites, particularly in connection with themanufacture of laminates. In that case the polymer combination, can onthe one hand, as already outlined, be used as a straight adhesive, whileon the other hand the bonded polymer acts with particular advantage asan interlayer, particularly as a water-vapour-permeable interlayer.

The adhesion mechanism on which the invention is based can be describedas follows:

Films and powders comprising the polymer combination described are polarby virtue of the aforementioned free carboxyl groups which aredistributed over the whole length of the polymer chain of the continuousphase. This means that they are hydrophilic, and hence possess a highaffinity for water. Consequently, depending on hardness and the amountof free carboxyl groups, they are able to absorb water. In doing so, thepolymer has incorporated into it water molecules, which act asplasticizers and increase the mobility of the polymer chains. Films andpowders become soft and tacky and can in this state be applied to avariety of substrate surfaces. The high polarity of the polymercombination allows a firm bond to the substrates. As a result of thesubsequent drying process the plasticizer effect is lost and theoriginal state of the polymer combination is reestablished. Adhesion tothe substrate surface, however, is retained.

The preparation of the acrylic and/or methacrylic acid polymer takesplace as described in patent EP 0 928 316 B1, it being possible to givepreference, rather than a polymerization in the melt, to a solutionpolymerization in organic solvents, which can lead to molecular sizeswhich are favourable, in particular for the adhesive properties.

The polymer combination is preferably compounded, as described in EP 0928 316 B1, in the melt.

Further features of the invention will emerge from the followingdescription of preferred embodiments in conjunction with the dependentclaims. In these embodiments the individual features may each berealised individually, or two or more thereof in combination with oneanother, in an embodiment of the invention.

EXAMPLES

The hardness and the hydrophilic nature of the two-phase polymercompound can be adjusted by way, inter alia, of the composition of theCOOH-containing matrix polymer (cf. Table 1). In the monomer mixture thefraction of α,β-unsaturated carboxylic acids is generally 20-40% byweight, preferably 25-35%. Esters of α,β-unsaturated carboxylic acidsare present in a fraction of 20-60% by weight, preferably 40-60%, andthe fraction of styrene, if present, is 5-50% by weight, in particular15-25%. As the styrene content goes up, for example, there is also adecrease in the water vapour permeability and the water absorbency ofthe films adjusted accordingly. TABLE 1 Composition and properties ofthe carboxyl-containing matrix polymer. Matrix polymer 1 2 3 4 Butylacrylate in % 57.5 52 48 20 Acrylic acid in % 27.5 29 30 33 (methacrylicacid) Styrene in % 15 19 22 47 Carboxyl content in % 16 17 18 18 Tg in °C. 45 50 61 110

The weight ratio of COOH-containing polymer to epoxy-containing impactmodifier in the film is from 9:1 to 1:1, in particular from 5:1 to1.8:1.

The compounding of the carboxyl-containing polymer with the impactmodifier takes place under computer control, it being possible to addvery-low-density polyethylene (VLDPE), anti-blocking agents such assilica or talc, lubricants such as stearic acid, stearamide orethylenamines and processing stabilizers from the class of thesterically hindered phenols to the mixture, at up to 10% by weight.TABLE 2 Composition and properties of films of the two-phase polymercombination. Film compound 1 2 3 4 5 Carboxyl-containing 55.5 61 58 6258 matrix polymer in % Epoxy-containing impact 40 35 40 35 40 componentin % VLDPE in % 2 2 2 Lubricant in % 1 2 1 2 Anti-blocking agent in %0.5 2 Stabilizer in % 1 Film A Film B Film C Film D Tensile strengthMD/CD 20/18 24/24 20/18 24/20 29/31 N/mm² Breaking elongation 250/300240/180 170/180 230/190 6/7 MD/CD % Water absorption % 16 10 10 14 <1Water vapour 85 40 50 66 <5 permeability g/m²/24 h Tg in ° C. 46 46 5059 98

Selected films were used for adhesive tests with neutral water, theresults being as follows: TABLE 3 Assessment of adhesion: 1 - filmundetachable; 2 - film difficult to detach, partially fractures; 3 -film difficult to detach, no fracture; 4 - film easy to detach; 5 - noadhesion. Film (% styrene) A (8) B (11) C (14) D (30) Glass 1 2 2 5Aluminium 1 3 4 5 LDPE 4 5 5 PP nonwoven 5 Stationery paper 4 High-glosspaper 4 Steel, stainless 2 Steel sheet, galvanized 2

Further experiments investigated the adhesion which occurred whenbonding film to film. TABLE 4 “Film-to-film” adhesion tests. Adhesion isassessed as in Table 3. Film on film A B C D A 1 1 1 1 B 1 1 1 1 C 1 2 45 D 1 1 5 5

By moistening with 0.5% strength sodium hydroxide solution it is alsopossible for films A, B and C to be bonded effectively to aluminium,stationery paper and galvanized steel sheet. The adhesion is unaffectedby accelerated drying in a drying cabinet at 40° C.

1. An adhesive composition dissoluble in aqueous alkali, comprising inga two-phase polymer combination being capable to form an adhesive bondto substrates in moist state whereas being non-tacky in dry state andsaid polymer combination consisting essentially of a. an alkali-solublecopolymer or terpolymer of an α,β-unsaturated monocarboxylic acid whichpossesses carboxyl groups distributed essentially uniformly over thechain of the molecule, as a continuous phase, and b. a copolymer orterpolymer which is insoluble in aqueous alkali and contains epoxygroups along its polymer chain, as a discontinuous finely dispersephase, wherein free epoxy groups on the surface of the polymer particlesof the discontinuous phase are linked by esterification with some of thecarboxyl groups of the polymer of the continuous phase, and theremaining carboxyl groups are present in unchanged form, wherein theadhesive composition can be made tacky by addition of aqueous moisture.2. Adhesive composition according to claim 1 wherein the aqueousmoisture is provided in form of an aqueous liquid.
 3. Adhesivecomposition according to claim 1 wherein the polymer combination is inthe form of a film.
 4. Adhesive composition according to claim 3 whereinthe film is provided for bonding on at least one side.
 5. Adhesivecomposition according to claim 3 wherein the film is provided forbonding over its entire area.
 6. Adhesive composition according to claim3 wherein the film is provided for bonding only in part.
 7. Adhesivecomposition according to claim 3 wherein the film is transparent tomilky.
 8. Adhesive composition according to claim 3 wherein the film iscomprising pigments.
 9. Adhesive composition according to claim 3wherein the film is printed.
 10. Adhesive composition according to claim3 wherein the film is a detachable label.
 11. Adhesive compositionaccording to claim 3 wherein the film is a protective film for smoothsurfaces such as glass, metal, plastic and also coated surfaces. 12.Adhesive composition according to claim 3 wherein the film is a coating.13. Adhesive composition according to claim 12 wherein the film is aprotective coating against graffitiy.
 14. Adhesive composition accordingto claim 1 wherein the adhesive composition bonded to substrates isremovable without residue from the substrates by sufficient addition ofwater.
 15. Adhesive composition according to claim 1 wherein the polymercombination is in the form of particles.
 16. Adhesive compositionaccording to claim 15 wherein the polymer combination is in the form ofan aqueous dispersion.
 17. Adhesive composition according to claim 1wherein it is processable as a hot-melt adhesive.
 18. Adhesivecomposition according to claim 1 wherein it is processable in amulti-stage adhesion process in which the polymer combination is bondedmoist and in a further step bonded hot.
 19. Adhesive compositionaccording to claim 1 wherein it is processable as an adhesive inlaminating operations.
 20. Adhesive composition according to claim 1wherein it is an interlayer between at least two layers of a composite.21. A method for bonding a two-phase polymer combination dissoluble inaqueous alkali to a surface of at least one substrate, said two-phasepolymer combination consisting essentially of a. an alkali-solublecopolymer or terpolymer of an α,β-unsaturated monocarboxylic acid whichpossesses carboxyl groups distributed essentially uniformly over thechain of the molecule, as a continuous phase, and b. a copolymer orterpolymer which is insoluble in aqueous alkali and contains epoxygroups along its polymer chain, as a discontinuous finely dispersephase, wherein free epoxy groups on the surface of the polymer particlesof the discontinuous phase are linked by esterification with some of thecarboxyl groups of the polymer of the continuous phase, and theremaining carboxyl groups are present in unchanged form, comprising thesteps of: providing said two-phase polymer combination, supplyingaqueous moisture to said polymer combination and applying the moistpolymer combination to said surface of said at least one substrate. 22.Method according to claim 21 wherein the aqueous moisture is provided inform of an aqueous liquid.
 23. Method according to claim 21 wherein theapplication of the moist polymer combination is followed by a dryingphase.
 24. Method according to claim 21 wherein the polymer combinationis applied in the form of a film.
 25. Method according to claim 24wherein aqueous moisture is supplied to one side of the film to provideit for bonding on said side.
 26. Method according to claim 24 whereinaqueous moisture is supplied to both sides of the film to provide it forboth-side bonding.
 27. Method according to claim 24 wherein aqueousmoisture is supplied to the entire area of the film providing it forbonding over its entire area.
 28. Method according to claim 24 whereinaqueous moisture is supplied to certain places of the film providing itfor bonding only in said places.
 29. Method according to claim 21wherein the polymer combination is provided in the form of particles.30. Method according to claim 29 wherein the polymer combination isapplied in the form of an aqueous dispersion.
 31. Method according toclaim 21, comprising a further step in which the polymer combination isbonded as a hot melt under heat subsequent to the application of themoist polymer combination.
 32. A method to remove a two-phase polymercombination bonded to a substrate from said substrate without residue,said two-phase polymer combination consisting essentially of a. analkali-soluble copolymer or terpolymer of an α,β-unsaturatedmonocarboxylic acid which possesses carboxyl groups distributedessentially uniformly over the chain of the molecule, as a continuousphase, and b. a copolymer or terpolymer which is insoluble in aqueousalkali and contains epoxy groups along its polymer chain, as adiscontinuous finely disperse phase, wherein free epoxy groups on thesurface of the polymer particles of the discontinuous phase are linkedby esterification with some of the carboxyl groups of the polymer of thecontinuous phase, and the remaining carboxyl groups are present inunchanged form, comprising the step of: supplying aqueous moisture tosaid bonded polymer combination.